Network Timers for Incoming SIP trunks


I woudl appreciate any assistance on these matters.

I am currently running Asterisk 1.4.9 and have been struggling on 2 fronts with calls coming in from my SIP trunk to a connected SIP peer.

First problem is when the call is not answered at the SIP Peer, the call is released with a SIP 486 Busy Here. I would like to change it to send back a SIP 480 Temporarily Unavailabe.

Second, If I reject a call without answering I would like to send back a SIP 603 to the Trunk.

Third and Final at this moment in Time, is where and how are the Trunk Network Timers specified. I can understand how the Peer timers are handled, but where ‘O’ where are the Incoming Trunk Network timers.